Project Summary/Abstract The best approach to identify risk and protective factors, and develop early biomarkers, of cognitive decline and dementia in older people is to conduct prospective longitudinal studies of aging in representative cohorts from the population. Many such studies are being conducted around the world. For practical reasons, no single study can have a large enough sample and sufficient power to detect modest-sized effects, or to compare rates, proportions, and antecedents in a large variety of populations. Further, these studies have used disparate methodologies, and even small variations in methodology make results difficult to compare across populations. This grant proposal is to support a consortium ? COSMIC (COhort Studies of Memory in International Consortium) ? that was established in 2012 and now includes 26 studies from 16 countries in five continents, with a combined sample size of >70,000. The leaders of these studies have agreed to pool de- identified data from these studies. The data harmonization strategy in COSMIC offers the potential to explore both existing and novel research questions by creating a single, large database to help minimize the influence of both study-level (e.g. methodology) and individual level (e.g. demographic) factors, while also enabling these to be explored as potential contributors to differences in results . Other advantages include increased statistical power for detecting effects of modest size, and the inherent replication and enhanced generalizability associated with using heterogeneous samples and methodologies. COSMIC will address many extant questions in the analytical epidemiology of cognitive aging and dementia. It will help examine the rates and patterns of cognitive decline in aging populations in diverse geographical regions and ethno-racial groups, and determine the prevalence and incidence of neurocognitive disorders in these settings. It will inform us which risk and protective factors are universal and others that are specific to certain populations. Novel factors may thereby be identified. Biomarkers of dementia can similarly be examined. The cohorts will permit the examination of decline in individuals who have been diagnosed with dementia, and the burden these disorders pose on the health care systems in different countries. COSMIC is a truly international effort. The rules of engagement have been established and the success of the first two projects has demonstrated its feasibility. This grant proposal is to help ensures its financial viability as it continues to grow to make a lasting impact on the epidemiology of cognitive aging and dementia.